Brooke Mueller's Twins Left With Denise Richards

Charlie Sheen's 2nd ex-wife Denise Richards got an interesting early XMAS gift -- twins ... but they're not hers ... they're Brooke Mueller's.

Sources close to Charlie and his exes tell TMZ ... Brooke asked Denise to care for Bob and Max while she tries rehab for the 19th time, and Denise happily obliged.

As for why Charlie isn't caring for the 3-year-olds ... we're told he doesn't have the time because he's shooting "Anger Management."

Our sources tell us ... Denise will care for Bob and Max for "an indefinite period of time."

It's pretty interesting ... not only is Brooke confident the kids will be well cared for, but Charlie is also happy Denise is taking care of his entire brood.

And get this ... we've learned this isn't the first time Bob and Max have stayed with Denise. The last time Brooke went to rehab, the kids stayed with D.R..